Refining of bismuth



United States Patent 3,010,821 REFINING 0F BISMUTH Robert Roland Platt, Rumson, and Lloyd Noel Poulsen,

Fords, N.J., assignors to American'Smelting and Refining Company, New York, N.Y., a corporation of New Jersey N0 Drawing. Filed Nov. 16, 1959, Ser. No. 853,005 12 Claims. (Cl. 75-70) This invention relates to a process for refining bismuth and especially to the further refining of refined bismuth.

More particularly, it relates to a process for the removal of small amounts of lead or nickel or admixtures thereof contained in bismuth.

Most, if not all, commercially refined bismuth is obtained by refining a crude bismuth-lead alloy. Such alloy typically contains from about 7 to 98% by weight of bismuth, although in some instances an alloy having a bismuth content above or below these values may also be encountered. Such crude alloy may be obtained from a number of sources. For example, it may be obtained electrolytically as a bismuth-lead alloy deposited at the cathode or by melting down the anode slimes obtained from the electrolytic refining of lead. A typical and comparatively large source of the crude alloy is as a crude bismuth-lead bullion obtained as a by-product from the pyrometallurgical refining of lead. ln the course of the pyrometallurgical refining of leadwhich contains bismuth, the molten impure lead is convention- 'ally treated in a suitable kettle With a conventional 'debismuthizing agent such as, for example, calcium or magnesium, to form a crude bismuth-lead bullion, which collects upon and is skimmed from the surface of the molten lead which is being refined.

The crude bismuth-containing alloy is conventionally refined in a molten state by a procedure involving chlorinating the alloy to remove lead therefrom. In general, when the alloy is a crude bismuthlead bullion obtained by the pyrometallurgical refining of lead or by 'melting down the anode slimes from the electrolytic refining of lead, such bullion is usually refined in'a plurality of steps which involve introducing zinc into the molten bullion to remove gold, silver, copper and nickel in a zincy dross which collects on the surface of the molten bullion and is skimmed therefrom; chlorinating the residual bullion to remove lead and any residual zinc therein as chlorides which also collect on the surface of the molten bullion and are skimmed therefrom; and treating the remaining molten bismuth with a molten slag comprised of an alkaline compound of an alkali metal such as, for example, sodium hydroxide or sodium carbonate containing an oxidizing agent such as, for example, sodium nitrate, to incorporate the arsenic and antimony into the molten slag which is then removed from the molten bismuth. The thus refined bismuth is then cast into commercial shapes which are sent to market. Generally, in thus refining the crude bismuthlead bullion, the latter, if it contains less than about 50% bismuth, is first chlorinated to remove sufiicient lead therefrom to raise its bismuth content to 50% or more before the zinc introduction step is practiced.

The above and other procedures available to the art' are incapable of producing consistently a bismuth product containing 99.999% or more of bismuth. In particular, they are deficient in that they-are incapable of sufiicient 3,910,3Zl Patented Nov. 28, 1961 ice removal of nickel from the bismuth and are not reliably efiective in removing sutficient lead therefrom. Heretofore, when a bismuth product having a purity of 99.999% or more has been desired, the art has been reduced to the practice, for want of a better procedure, of repeating the prior refinement procedures and literally hoping for the best as to improvement in purity of the rerefined bismuth.

One of the advantages of the invention is that if overcomes the above-metnioned difiiculties of the prior art. Another advantage is that it provides a process for removing nickel and lead from bismuth, which process is especially advantageous in further reducing the relatively small amounts of nickel and lead which persist in the bismuth refined by the bismuth refinin procedures presently available to the art. A further advantage of the invention is that it affords a simple and cheap process for the further refining of refined bismuth. Another advantage is that it afiords a process in which bismuth having a purity in excess of 99.999% is readily and consistently produced. These and other advantages will become apparent to those skilled in the art from the following more detailed description of the invention.

In one aspect, the invention comprehends the step, in the refining of bismuth, of incorporating phosphorous into a molten bath of bismuth and separating the resulting dross from the bath, to further refine the bismuth. In another aspect, the invention comprehends incorporating phosphorous into a molten bath of bismuth containing either or both nickel and lead to form a dross containing nickel or lead, or both if both are present in the bismuth, and then separating the thus formed dross from the molten bismuth. The dross, being lighter than the bismuth, fioats on the surface of the latter and may be removed therefrom in any suitable manner, but preferably is removed by skimming. Decreased temperature of the molten metal bath facilitates formation and collection of the dross upon the molten metal. Preferably, therefore, the dross formation step is conducted while maintaining the temperature of the metal bath substantially at or slightly above its freezing point.

In practicing the invention, phosphorous may be incorporated into the molten bath by adding thereto a phosphorous yielding material which may be elemental phosphorous as such or a material which forms phosphorous in situ in the molten bath. Thus, elemental phosphorous or a phosphorous alloy, for example, a phosphor-tin alloy or other suitable alloy, may be added to the bath to incorporate phosphorous therein. In general, phosphorous alloys are not preferred although they may be employed with advantage Where the component or components alloyed with the phosphorous are desirable in the bismuth or any residual amounts thereof remaining in the bismuth are not objectionable therein. The phosphorous yielding material may also comprise a phosphorous compound. Preferably, such compounds are relatively unstable phosphorous compounds, for example, compounds such as comparatively reactive phosphorous sulphides, chloride, oxychlorides, phosphoric acids, and phosphates, such as, for example, P 8 P 8 P 8 PCI POC1 H PO H PO HPOQ,

etc. Such compounds characteristically possess melting points below 1200" F., generally well below 800 F.

NaH PO 11-1 0, Na HPO -7H O, Na PO l2H O N214P2O7' 101-1 0, Na HPO -5H O etc. However, for best results, these latter type compounds are employed in conjunction with an added reducing agent. Any suitable reducing agent, such as, for example, carbon or a reactive metal, may be used where an added reducing agent is employed. Preferably, the added reducing agent is a reactive metal such as zinc, magnesium or aluminum which is readily removable from bismuth by the refining procedures of the prior art. Elemental phosphorou or a phosphorous sulphide, especially P 5 are the P eferred phosphorous yielding materials; elemental red phosphorous being at present the most preferred material.

The amount of phosphorous yielding material employed will depend upon the amount of the impurities, especially nickel and lead, which is contained in the bismuth and the amount of such contained material that it is desired to remove. In general, especially in further refining refined bismuth, elemental phosphorous or equivalent phosphorous material is added to the bismuth in amounts elfective to dross ofi impurities therefrom, and preferably in amounts to substantially eliminate or reduce nickel and lead from the bismuth. Bismuth which has been refined by the refining procedures heretofore available usually possess a purity which is less than 99.999% and generally above 99.990%. Normally, such bismuth contains nickel or lead and usually both, in amounts from more than .0001% up to 005% of each, although in some instances it may contain up to as much as .0l% or more of each. Generally, in further refining such bismuth in accordance with the process, about 0.3 to 2.4 pounds of elemental phosphorous or its equivalent per ton of bismuth are used. Preferably, within this range 0.4 to 2.0 pounds of elemental phosphorous or its equivalent per ton of bismuth are used.

Phosphorous may be incorporated into the molten bath in any desired manner. For example, phosphorousyielding material, including an added reducing agent where the latter is used, may be stirred into the bath or it may be submerged in the bath in a suitable container or basket through which the bismuth metal may be circulated by stirring or by moving the basket up and down in the bath. Preferably, it is added in a plurality of increments to a vortex established by conventional mixing apparatus.

The process maybe conducted at any desired temperature. However, the temperature of the molten bath during the phosphorous incorporating step is preferably maintained below 1200" F., and for best results, substantially at the freezing point of the bismuth metal of the bath, for example, within about 15 F. ofthe freezing point of the bismuth metal, as is indicated by the formation of a solidified n'm at the surface perimeter ofthe bath.

'For convenience in drossing, the dross may be removed from the bath by stopping the stirring, heating the bath sufliciently to loosen the solidified rim from the sides of the kettle or other container in which the process is practiced, this latter usually being accomplished by heat- 1 ing the hath not in excess of about 100F. above the melting point of the bismuth metal, and then skimming :been added and the second afterthe rest of the phosphorous has been added. If desired, the rim loosening step can be dispensed with, in which case the bath may be drossed and the remaining molten bismuth removed therefrom without disturbing or detaching the rim from the kettle.

The invention is further illustrated in the accompanying examples. It should be understood, however, that the examples are given for purposes of illustration and the invention in its broader aspects are not limit-ed thereto.

EXAMPLE 1 20,000 pounds of bismuth contaminated with 0.0005 each of nickel and lead as determined by spectrographic analysis were melted ina conventional cast iron kettle equipped with a conventional burner and a mixer. After the metal was melted its temperature was adjusted to a value slightly above its freezing point of 520 C. as indicated by a slight crusting over the liquid surface and the formation of a solidified of the bismuth metal at the surface perimeter of the kettle. The mixer was then started and its speed was adjusted to stir the molten metal sufficiently to produce a vortex on the metal surface. Six pounds of elemental red phosphorous in twelve substantially equal increments were then added to the vortex on the bath over a period of 15 minutes. Each increment was wrapped in a suitable covering material such as tissue paper which disintegrated and released the powdered phosphorous after it had been drawn below the surface of the molten metal. Each increment was added as soon as all burning from the previous increment had ceased; the interval between increment additions usually being on the order of about 30 seconds. During the phosphorous addition, the metal bath was maintained at a temperature in the range 520 to 525 F. as was indicated by the continued presence of the solidified rim on the bath surface. When the burning after the addition of the final increment of phosphorous had ceased, the mixer was stopped and the bath was heated sufiiciently to loosen the solidified rim, such loosening usually being accomplished by heating the bath to a temperature less than about 100 F above the melting point of the bismuth metal. Thereafter, the rim and all dross which had accumulated on the liquid metal. surface was carefully skimmed therefrom with a conventional perforated skimming tool. The bismuth metal remaining after the skimming step was again cooled to a temperature slightly above its melting point as indicated by the formation of the solidified rim on the surface perimeter of the bath and the phosphorous addition and skimming steps were repeated, again employing six pounds of elemental red phosphorous in twelve substantially equal increments during the second phosphorous addition step. After the second drossing step the remaining bismuth metal in the kettle was sampled and analyzed. It was found to contain less than 0.000l% lead and no deteotable amount of nickel, by spectrographic analysis.

EXAMPLE 2 Crude bismuth-lead bullion containing 35% bismuth, 64% lead, 001% silver, .0005 copper, .0005 nickel, 02% arsenic, and ;5% antimony was refined in the following conventional manner: 50 tons of the crude bullion was melted in a cast iron kettle provided with a suitable burner and a stirring device. Gaseous chlorine was introduced beneath the surface of the molten bullion to remove therefrom sufiicient lead as lead chloride to increase the bismuth content of the bullion to 50%. The lead chloride which collected on the surface of the bullion was removed therefrom by skimming. Thereafter, 30 pounds of'zinc per ton of remaining bullion were added and stirred into the remaining bullion while maintaining the temperature of the molten metal at about 850 to 900 F. 'The bath was then gradually cooled to its freezing point to form and liquate therefrom a zincy dross containing silver, copper and nickel from the bullion; the dross being removed by skimming from the bath as the dross collected thereon during the gradual cooling. The molten bullion remaining after the zinc drossing step was again chlorinated; the addition of the gaseous chlorine beneath the surface of the molten bullion being continued at least until voluminous fumes of bismuth chloride began to appear, to remove as much as practicable of the lead contained in the bullion as lead chloride which collected on the surface of the metal and was removed therefrom by skimming. Thereafter, the chlorine addition was stopped and the remaining metal was treated with a molten caustic soda and niter slag to remove the arsenic and antimony from the metal by heating the latter to 850950 F. and adding to the metal, in three substantially equal increments, a total of 25 pounds of caustic soda and pounds of sodium nitrate, per ton of remaining metal. The metal was stirred for one hour after the addition of each increment While maintaining the molten bath at a temperature of 850950 F. and thereafter, at the end of each hour period, the molten slag was skimmed from the surface of the bath. The refined bismuth recovered from the foregoing procedure was found to be 99.998% pure and to contain 0.0002% silver, .O005% lead, 0.0003% copper, 0.0005% nickel and 0.0001% iron by spectrographic analysis.

The thus refined bismuth was further refined in accordance with the invention, employing the procedure described in Example 1 using a total of 1.2 pounds of red phosphorous, per ton of the refined bismuth. After the second dross skimming step was completed, the remaining metal was treated with a molten caustic soda and niter slag in the manner described above in this Example 2, employing a total of 25 pounds of caustic soda and 10 pounds of sodium nitrate, per ton of metal, to insure the removal of any excess phosphorous remaining in the further refined bismuth metal. The thus refined bismuth was found to have a purity in excess of 99.999% bismuth and to contain by spectrographic analysis 0.0002% silver, 0.0001% iron, less than 0.0001% copper, less than 0.0001% lead, and no detectable amount of nickel.

Over a period of months all of the conventionally refined bismuth produced in a commercial plant was further refined as described in the preceding example. The bismuth metal obtained before the phosphorous incorporating step typically contained .001 to .005% each of lead and nickel together with a total amount of other detectable impurities up to about .0O09%. Typically, such other detectable impurities were silver, copper and iron which usually were present in amounts less than about .0005% of each. It was found that the purity of the further refined bismuth product after the phosphorous incorporating step was consistently above 99.999% and contained less than 0.0001% each of lead, nickel and copper.

EXAMPLE 3 The procedure described in Example 2 was repeated using phosphorous penta sulphide as the phosphorous yielding material in a total amount of 2 pounds of P 5 per ton of bismuth in the phosphorous incorporating step. The bismuth obtained before the phosphorous incorporating step was less than 99.999% pure and contained .0003% silver, .O001% iron, .0006% copper, 002% lead and 005% nickel. The bismuth product obtained after the phosphorous incorporating step was more than 99.999% pure and contained .0002% silver, .0001% iron, .0001% copper, .000l% lead and no detectable amount of nickel.

in the following examples the procedure described in Example 1 was repeated with refined bismuth obtained Table l Phosphorous-yielding Per- Per- Per- Per- Per- Ex. material cent cent cent cent cent lead nickel copper silver iron 41 Phosphorous pcuta sulphide 0001 .0001 0001 0002 0001 5. 5. Phosphorous hcpta sulphide 0001 0001 0001 .0002 .0001

7. 6- Plipssphorous sesqui sulphide 0005 001 001 0002 0001 4 3- 7.- Plgacslpshorous penta chloride 0002 0005 0028 .0004 0001 8. Phosphoric acid H;PO4 0001 .0001 .003 0004 .0001 9 Ortho phosphoric acid .0005 .001 .003 .0004 .0001 10 Plggrbhlorous oxychloride .0015 001 0028 .0004 .0001

3. 111 Mfeltla O phosphoric acid 0005 001 003 0004 .0001

3. 121 Sodium ammonium phos- .0008 .0015 .003 0004 .0001

phate NaNH PO AH2O.

Comparable removal of lead and nickel are obtained with relatively stable phosphorous compounds such as are exemplified by P 0 PCl Na PO KH PO NaH PO IHZO, Na2HPO4.7H O, Na PO 121 120, Na P O- JOH O, and Na HPO .5H O by employing such a compound together with a suitable reducing agent, such as carbon or a reducing metal such as zinc, magnesium or aluminum, as the phosphorous-yielding material in the phosphorous incorporation step.

What is claimed is:

1. In a process for producing refined bismuth from a crude bismuth-lead alloy which involves establishing a molten bath of said alloy, chlorinating the alloy to form a chloride dross on said bath, removing the chloride dross therefrom, and recovering a refined bismuth product from the bath, the improvement which comprises further refining the bismuth by incorporating phosphorous into the molten bath, and separating the resulting dross from the metal bath.

2. A process according to claim 1 in which elemental phosphorous is added to said bismuth.

3. A process according to claim 1 in which a phosphoric acid is added to said bismuth.

4. A process according to claim 1 in which a sulphide of phosphorous is added to said bismuth.

5. A process according to claim 2 in which said elemental phosphorous is red phosphorous.

6. A process according to claim 3 in which said phosphoric acid is H PO 7; A process according to claim 4 in which said sulphide is phosphorous penta sulphide.

8. A process according to claim 4 in which said sulphide is phosphorous hepta sulphide.

9. A process according to claim 4 in which said sulphide is phosphorous sesqui sulphide.

10. A process according to claim 1 in. which said molten bath of bismuth is maintained substantially at its freezing point during the incorporation of the phosphorous therein.

11. A process according to claim 10 in which a rim of solidified bismuth is present at the surface perimeter of the bath during the incorporation of the phosphorous, the bath is heated sufficiently to loosen said rim from the sides of the container of the bath after the phos- '7 8 pho ons has been incorporated into the bath, and there- References Cited in the file of this patent after the dIOSS iS skimmed from the bath. UNITED STATES PATENTS 12 A process for refining bismuth to remove therefrom a contained metal impurity selected from th rou 1,809,871 mg June 1931 consisting of nickel, lead and mixtures thereof whi h 5 1870388 1932 comprises establishing a molten bath of said bismuth, OTHER CES incorporating phosphorous into the molten bath to form Eisslar: Metallurgy of Gold, Crosby Lockwood and a dross containing said contained metal, and separating Son, Londcn, 1900 (pages 596 597) the dross fronmfthe molten bismuth. 

1. IN A PROCESS FOR PRODUCING REFINED BISMUTH FROM A CRUDE BISMUTH-LEAD ALLOY WHICH INVOLVES ESTABLISHING A MOLTEN BATH OF SAID ALLOY, CHLORINATING THE ALLOY TO FORM A CHLORIDE DROSS ON SAID BATH, REMOVING THE CHLORIDE DROSS THEREFROM, AND RECOVERING A REFINED BISMUTH PRODDROSS THEREFROM, AND RECOVERING A REFINED BISMUTH PROUCT FROM THE BATH, THE IMPROVEMENT WHICH COMPRISES FURTHER REFINING THE BISMUTH BY INCORPORATING PHOSPHOROUS INTO THE MOLTEN BATH, AND SEPARATING THE RESULTING DROSS FROM THE METAL BATH. 